ok im new to the hole nitro engines thing. not really new to the whole tunning process of them, but when it comes to running different shims under the button, how do you know how many to run? i am running a p3 plug in a GO .21 3 port and right now it has 2 brass shims and the 1 aluminum shim and i am running 30% byrons fuel.

also i just got a new piston/sleeve/conrod for it as it is about to go out here soon. will i be ok breaking in these new parts with 30% fuel? i cant find 20% anywhere. no one around my parts sells anything less than 30%

thanks for the help